In the disclosure of the present invention reference is mostly made to the treatment of diabetes by delivery of insulin, however, this is only an exemplary use of the present invention.
Drug Injection devices have greatly improved the lives of patients who must self-administer drugs and biological agents. Drug Injection devices may take many forms, including simple disposable devices that are little more than an ampoule with an injection means or they may be highly sophisticated electronically controlled instruments with numerous functions. Regardless of their form, they have proven to be great aids in assisting patients to self-administer injectable drugs and biological agents. They also greatly assist care givers in administering injectable medicines to those incapable of performing self-injections.
In particular pen-style injection devices have proven to provide an accurate, convenient, and often discrete, way to administer drugs and biological agents, such as insulin. Modern devices have become more sophisticated and often include diverse and robust functions, such as memories for remembering time and amount of last dose, as well as, in the case of insulin devices, blood glucose monitors. While pen-style injection devices are typically cylindrically shaped with a needle protruding from the most distal portion of one end of the device, some devices have other shapes with the needle no longer protruding from the most distal part of an end of the device, e.g. Innovo® and InnoLet® from Novo Nordisk A/S, Bagsvaerd, Denmark.
Typically, injection devices use a pre-filled cartridge containing the medication of interest, e.g. 1.5 or 3.0 ml of insulin or growth hormone. The cartridge is typically in the form of a generally cylindrical transparent ampoule with a needle pierceable septum at one end and an opposed piston designed to be moved by the dosing mechanism of the injection device. The injection devices generally are of two types: “Durable” devices and “disposable” devices. A durable device is designed to allow a user to replace one cartridge with another cartridge, typically a new cartridge in place of an empty cartridge. In contrast, a disposable device is provided with an integrated cartridge which cannot be replaced by the user; when the cartridge is empty the entire device is discarded. Most injection devices are provided with a releasable pen cap covering and protecting the cartridge, the needle mount portion with the pierceable septum, and, as may be the case, a mounted needle. To protect the needle it is normally provided with an inner needle cap.
Normally insulin formulations are provided with a concentration of 100 IU/ml, i.e. 300 UI in a 3 ml cartridge. This said, it may be desirable to provide a given drug in different concentrations, e.g. a given type of insulin may be provided in cartridges having a concentration of either 100 IU/ml or 200 IU/ml, the latter providing that for a given dose amount of active drug only half the volume has to be delivered.
WO 2012/022771 discloses an electronically controlled drug delivery system adapted to detect a property of a cartridge. The property may be drug concentration allowing the system to vary the volume of drug dispensed to allow for varying drug concentration. EP 1 095 668 discloses an electronically controlled drug delivery system adapted to detect the diameter of a cartridge and calculate the distance the piston has to be advanced in order to expel a given amount of drug.
However, disregarding electronically controlled infusion pumps which may be set in accordance with drug concentration, traditional mechanical drug delivery devices are designed to expel a fixed volume of drug for each increment of the dose setting mechanism, e.g. a set insulin dose of 30 IU will result in 0.3 ml of insulin formulation to be expelled. Correspondingly, a specifically adapted drug expelling device would have to be provided for each concentration of drug just as it has to be ensured that a given drug cartridge cannot be used in the wrong device.
Having regard to the above, it is an object of the present invention to provide a drug delivery system having a mechanical expelling mechanism and which in a cost-effective manner allows a given drug to be supplied in cartridges having different concentrations. The device should be simple, safe and convenient to use.